It is the function of pipette tip racks to organize disposable pipette tips in a manner for convenient tip placement on a pipette. Such racks generally comprise a base with vertical sides joined at contiguous edges and containing supports for a rigid horizontal tray or support plate containing an array of holes for vertically receiving and supporting a horizontally spaced array of pipette tips. The pipette tips are held vertically in the array for ease of access by a pipette tip user. In this regard, the pipette tip user simply moves a hand-holdable pipette over the rack and lowers a distal end of the pipette into a proximal or upper end of a vertically oriented tip and presses down to affix the tip to the pipette. A similar operation is followed by the user when connecting a plurality of tips to a multiple tip pipette. U.S. Pat. No. 4,676,377 describes a conventional pipette tip rack of the type just described, and U.S. Pat. No. 4,779,467 describes a multiple tip pipette.
Once all tips are dispensed from the tip rack, the rack may be discarded or reloaded with a new supply of pipette tips. The reloading of disposable pipette tips into such tip racks in a rapid, convenient manner is important to pipette users. Further, any packaging containing pipette tips and for use in loading pipette tips into a tip rack should arrange the pipette tips in a manner to accommodate direct dispensing of the tips into standard tip rack arrangements. Moreover, it is important that such packaging protect the disposable pipette tips from damage and contamination during shipping, handling and storage and provide for sterilization by autoclaving or irradiation of the pipette tips. Still further, when plastic materials are utilized for such packaging, it is particularly important to the preservation of our environment (1) that the plastic material be recyclable and (2) that the packaging structure be thin, lightweight and of low mass to minimize the amount of non-biodegradable disposable material from such packaging. Furthermore, there is a need for refill packs for manually reloading reusable pipette tip racks with filter containing pipette tips such as the FilterPro of the Rainin Instrument Co., Inc., assignee of the present invention, or, such as the filter devices described in U.S. Pat. No. 5,156,811, assigned to Continental Laboratory Products, Inc. of San Diego, Calif.
Prior packaging used for stacks of pipette tip racks and for pipette tips for reloading empty pipette tip racks do not satisfy such requirements. For example, U.S. Pat. No. 3,853,217 describes a stack of stand-alone pipette tip racks, referred to in the patent as "trays". Each tray comprises a horizontally oriented rectangular support. The horizontal support contains transverse stiffening ribs. Each rib extends above the horizontal support and terminates in marginal vertical sides. The sides extend above and below the horizontal support and connect at their contiguous edges to form a skirt. The skirt extends below distal end portions of vertical pipette tips contained in a honeycomb array of openings in the horizontal surface. A shoulder is formed around the skirt so as to accept and support an identical upper tray to rest a lowermost edge of its skirt for stacking of the trays. The shoulder thereby spaces the upper tray so as to allow the distal end portion of the pipette tips in the upper tray to extend into the open proximal end of the pipette tips in the lower tray. Concentric positioning of the upper tips in the lower tips permits a nested stacking of multiple trays. A cover encloses the topmost tray in the stack. Tape is used to secure the cover and stacked trays; applied to fasten the cover and trays along common sides. Nested stacks of the trays with a cover are enclosed within a snug carton for shipping and storage. Additionally, folded sleeves are included in the shipping carton for covering a tray removed from the stack. The carton is provided with a pipette tip extractor for collecting used tips in the shipping carton. The trays are structurally rigid and with sufficient material thickness to be self supporting. The rigid trays are used individually and stored as stacked.
In use, the stacked trays with the cover taped in place are removed from the shipping carton. Individual trays are removed from the bottom of the stack by severing the tape attaching the lowest tray, leaving the upper trays attached and enclosed until the next bottom tray is to be used. The pipette tips are accessed individually from the tray, since the honeycomb arrangement does not accommodate multiple tip pipettes. Used pipette tips are disposed of in the shipping carton, using the tip extractor included. As each tray is emptied, it is discarded. Since the trays are intended for stand-alone use, their structure is necessarily heavy, with thick stiffening sections, containing a significant amount of plastic. Therefore, the heavy trays represent a significant environmental disposal problem. Further, the nesting of the trays with upper pipette tips extending into lower tips, precludes the use of the package of U.S. Pat. No. 3,853,217 for storage and dispensing of filter containing pipette tips.
In U.S. Pat. No. 3,937,322, a package containing a stack of trays of pipette tips is disclosed. Each tray comprises a horizontal rectangular support with an array of openings. The openings accept distal end portions of pipette tips and maintain their longitudinal axes in a vertical orientation. The trays are stacked in a carton by telescoping the pipette tips carried by an upper tray into the open upper ends of the pipette tips carried by the next lower tray and by resting a horizontal support lower surface of the upper tray on the upper edge of the pipette tips in the next lower tray. The lowermost tray in the stack is supported on a tray support extending vertically from a bottom of the carton. Also attached to the carton is a pipette tip extractor.
In use, the carton is opened at the top and uppermost pipette tip trays are exposed. The pipette tips are accessed from the open top of the carton and individually loaded onto pipettes. This is accomplished by pressing an end of a pipette into a tip to seat the tip thereon and then by removing the loaded pipette from the carton. When all the pipette tips on the uppermost tray have been thus dispensed from the tray, the tray is discarded, exposing the tips in the tray below. The pipette tip extractor is installed in a wall of the carton and permits a used tip to be extracted from the pipette and dropped into the carton without contact with the user. The carton is then used for disposal of used tips.
As described, the container of U.S. Pat. No. 3,937,322 is characterized by a number of shortcomings. Because of the telescoping of the pipette tips in the stack of trays, it is not possible to use the packaging of the '322 patent for the storage and dispensing of filter containing tips. Further, for one of the contained pipette tips to be accessible to a user for reloading of a pipette, substantially all the contained pipette tips are exposed to the atmosphere and hence subject to possible contamination. Finally, each tray is supported on the tops of the pipette tips in the next lower tray. Unless the trays and the bottom tray support are formed of relatively heavy, rigid plastic or equivalent material, the downward pressing of the pipette in loading a tip onto the shaft of a pipette will produce an undesired downward bowing of the trays. The bowing of the tray makes it difficult to insert a pipette onto the end of a pipette shaft. In the case of a multiple-tip pipette, only a small amount of bowing is required to prevent a user from being able to insert pipette tips simultaneously onto all shafts of the multiple-tip pipette simply by pressing down on the pipette. Rather, if the tray bows, a user must (i) check each tip individually in order to assure that all tips are properly secured to each pipette shaft and (ii) secure any loose tips individually by hand. With a heavier, more rigid rack support, such bowing will not occur. However, if the trays and the bottom tray support are formed of a heavy rigid plastic material to prevent such undesired bowing during the loading of pipettes, then the disposal of such trays will present an undesired increase in the disposal of non-biodegradable materials.
Prior commercially available packaging of stacks of nested pipette tip racks similar to the packaging disclosed by the U.S. Pat. No. 3,853,217 and possessing all the disadvantages thereof is represented by the RBR Packaging of Bio-Rad Laboratories, Inc. of Richmond, Calif. TBR Packaging comprising a stack of separate racks is also available from Bio-Rad Laboratories, Inc. In addition, USA/Scientific Plastics of Ocala, Fla. markets a RE-PACK RACK comprising a reusable pipette tip rack, designed to accept RE-PACK Tray Cartridges preloaded with 192 pipette tips per tray. Once a tray is empty, it is simply removed from the rack and discarded and another tray cartridge inserted in its place. The RE-PACK Tray Cartridges are formed of a rigid, relatively heavy plastic construction and, but for the transverse ribs, resemble and possess the disadvantages of the trays disclosed in U.S. Pat. No. 3,853,217. Such RE-PACK tray cartridges are available in shrink-wrapped stacks of 5 trays of 192 tips each.
From the foregoing, it should be appreciated that prior packages for pipette tip racks and trays do not satisfy the previously stated desired requirements for packaging for reloading of disposable pipette tips into reusable tip racks. Thus, there is a continuing need for such packaging which is satisfied by this present invention.